As the field of gravitational wave (GW) astrophysics matures, the growing amount of data is being used in a variety of ways and in different contexts to solve problems in topics like fundamental physics, astrophysics, and cosmology.
One critical subject that has drastically benefited by the observation of GWs is the study of the gravitational interaction.
General relativity (GR), our best theory of gravity to date, has some shortcomings, if we may call them that [1]}, [2]}.
These include the incompatibility of GR with quantum mechanics (c.f. Ref. [3]}) and the singularity problem [4]}, [5]}, as examples.
Aside from these shortcomings, the theory also struggles to adequately explain certain phenomena observed in our universe without the inclusion of additional structure, like the late time acceleration of the universe (unless one includes an “unnaturally” small cosmological constant)  [6]}, [7]}, the rotation curves of galaxies (unless one includes dark matter particles that have so far been undetected via direct experiment) [8]}, [9]}, and the matter-antimatter asymmetry of the universe (unless one includes new parity-violating interactions that satisfy the Sakharov conditions) [10]}.
Modifications to GR in the ultraviolet or in the infrared may potentially resolve some of these theoretical and observational issues, which is why they have attracted attention lately in light of new GW data.
